Generalized Multiprotocol Label Switching (GMPLS) and Automatically-Switched Optical Network (ASON) standards are driving increasing levels of dynamic optical network reconfigurability. Optical signal propagation is an inherently analog process, and monitoring analog network performance is critical to dynamic reconfigurability. Both optical network design and reconfiguration require the use of optical path computation software that computes expected signal performance based on specific network physical characteristics. An example of such path computation software is the Path Computation Element (PCE) currently under consideration in the IETF. These must still be validated against field measurements, as there are large uncertainties in the optical fiber and installed equipment as well as possible aging errors. Networks may have wavelengths with several technology generations supporting a variety of data rates, modulation formats, and the like.
The current state of the art in deployed networks is limited to three types of measurements. First, existing channels provide a measure of both pre-corrected and post-corrected Forward Error Correction (FEC) error counts. These are only available for specific lightpaths, where channels with embedded FEC are already installed and operational. Further, pre-FEC bit error rate (BER) is only accurate at high values. At lower values of BER, the counts only provide an upper bound measurement due to the presence of dynamic control algorithms, which stop working once a specific bound is reached. Finally, no information is provided that can be used to predict the performance of channels with a different bit rate and modulation format.
Second, channel power levels are available at various points in the system, either as an aggregate total or for individual channels as at Optical Channel Monitor (OCM) points. These provide some indication of the overall system health, but can say very little about specific channel performance or about path suitability for additional channels. Third, some recent monitors have added Optical Signal-to-Noise Ratio (OSNR) measurement capability, which provides an indication of one of more major optical signal impairment mechanisms.
While some signal quality measurement approaches exist, they do not provide sufficient information to accurately estimate new channel performance, or to validate the accuracy of the path computation calculation. What is missing is ability to extract the following:                More accurate OSNR measurement;        Estimation for residual Chromatic Dispersion;        Estimation for Polarization Dependent Loss;        Estimation for Polarization Mode Dispersion;        Estimation for inter-channel nonlinear effects, such as Cross-Phase Modulation (XPM) and Four Wave Mixing (FWM);        Estimation for intra-channel nonlinear effects, such as Self-Phase Modulation (SPM), iXPM, iFWM; and        Estimation for possible bandwidth narrowing due to in-line optical filtering (for example, Optical Add-Drop Module (OADM) filters).        